Translesion synthesis (TLS) DNA polymerases (Pols) help ensure the continued progression of the replication fork by promoting replication through DNA lesions. In the proposed studies, we will determine the roles of a number of human TLS Pols in promoting replication through a variety of DNA lesions induced by environmental pollutants and carcinogens and by cellular oxidative damage. In particular, we will test the hypothesis that replication through DNA lesions in human cells occurs via two distinct modes in which Pols, ?, ?, k, Rev1, and ? mediate predominantly error-free TLS and act in a highly specialized manner dependent upon the DNA lesion, whereas Pol? performs lesion bypass in a more generalized and error-prone manner. Further, we will test the hypothesis that the more generalized and error-prone role of Pol? emanates from its ability to insert a purine nucleotide (nt), preferentially an A, opposite DNA lesions via a protein-template-directed mechanism. To elucidate the genetic bases of error-free and mutagenic replication through DNA lesions in humans, we will carry out the following studies. In Aim 1, we will examine the contributions of various TLS Pols to error-free vs. mutagenic lesion bypass in human and mouse cells. The lesions to be studied include (6- 4) photoproduct induced by UV irradiation, 7,8-dihydro-8-oxogunaine (8-oxoG) generated from free-radical attack on guanine in DNA, 1,N6-ethenodeoxyadenosine (edA) generated from interaction of adenine with products of lipid peroxidation resulting from cellular oxidative damage and from exposure to chemical carcinogens, 1,N2-propano-2'-deoxyguanosine (PdG), a ring-closed form of acrolein generated from lipid peroxidation and which also is a ubiquitous environmental pollutant, and N2-dG adduct of the environmental carcinogen (+) anti-benzo[a]pyrene diol expoxide (BPDE). In Aim 2, biochemical studies will be done to examine the proficiency of Pol? in synthesizing DNA opposite (6-4) TT photoproduct, 8-oxoG, edA, PdG, and N2-dG BPDE. By steady-state kinetic analyses we will determine the catalytic efficiency of Pol? for inserting nucleotides opposite the DNA lesion and for carrying out the subsequent extension reaction, and biochemical studies will be done to test the hypothesis that Pol? inserts a purine nt opposite DNA lesions via a protein- template-directed mechanism. The genetic and biochemical studies we propose here are highly relevant for delineating the roles of TLS Pols in promoting error-free vs. mutagenic lesion bypass during replication, and for providing a comprehensive understanding of the genetic bases of mutagenesis and carcinogenesis induced by environmental and cellular DNA damaging agents in human cells. Our proposal for a predominantly error-free mode of TLS by Pols ?, ?, k, Rev1, and ? would predict a role for these Pols in cancer suppression, whereas a mutagenic mode of TLS by Pol? would predict a role for this Pol in enhancing genomic instability and carcinogenesis.